Fournoi Korseon, commonly referred to as Fournoi, is a complex of small Greek islands located in the North Aegean region within the Ikaria regional unit. The archipelago is situated between the larger islands of Ikaria, Samos, and Patmos. Historically, the area has been known by various names, including Corsiae, Korsiai, Corseae, Korseai, Corsia, Korsia, and Corassiae.
The municipality covers a total area of 45.247 km2. The two largest islands in the complex are Fournoi, which measures 31 square kilometres, and Thymaina, which measures 10 square kilometres. While several islands make up the archipelago, only Fournoi, Thymaina, and the smaller Agios Minas Island (2.3 square kilometres) to the east are inhabited.
The town of Fournoi serves as the largest settlement on the main island and functions as the primary ferry harbour for the area. Ferries also provide access to the island of Thymaina. The second-largest settlement in the complex is located in the north of the main isle, known as Chrysomilia.